Orthopedic joint replacement surgery may involve arthroplasty of a knee, hip, or other joint (e.g., shoulder, elbow, wrist, ankle, fingers, etc.). For example, traditional total knee arthroplasty (TKA) involves a long incision, typically in a range of about 6 to 12 inches, to expose the joint for bone preparation and implantation of implant components. The invasive nature of the incision results in a lengthy recovery time for the patient. Minimally invasive surgery (MIS) reduces the incision length for a total knee replacement surgery to a range of about 4 to 6 inches. However, the smaller incision size reduces a surgeon's ability to view and access the anatomy of a joint. Consequently, the complexity of assessing proper implant position and reshaping bone increases, and accurate placement of implants may be more difficult. Inaccurate positioning of implants compromises joint performance. For example, one problem with TKA is that one or more components of the implant may improperly contact the patella, which may be caused by inaccurate positioning of the one or more implant components within the knee.
An important aspect of implant planning concerns variations in individual anatomies. As a result of anatomical variation, there is no single implant design or orientation of implant components that provides an optimal solution for all patients. Conventional TKA systems typically include a femoral component that is implanted on the distal end of the femur, a tibial component that is implanted on the proximal end of the tibia, and a patellar component that replaces the articular surface of the patella. As mentioned above, conventional TKA systems require an incision large enough to accept implantation of the femoral and tibial components. Further, the femoral and tibial components have standard, fixed geometries and are only available in a limited range of sizes. As a result, the surgeon may be unable to achieve a fit that addresses each patient's unique anatomy, ligament stability, and kinematics.
Modular TKA knee prostheses comprising multiple components that are inserted separately and assembled within the surgical site have been developed to overcome conventional TKA systems. Some modular TKA system implementations mimic a conventional TKA system by allowing the multiple components to be inserted separately so the components can be connected together inside the patient's body. One disadvantage is that the modular components, once assembled inside the patient's body, mimic a conventional TKA system and thus suffer from similar limitations. Once the modular components are fixed together, the components are dependent upon one another. Such implant systems do not enable the surgeon to vary the placement or geometry of each modular component to best suit each patient's unique anatomy, ligament stability, kinematics, and disease state.
Some modular TKA system implementations allow the implant components to be positioned independently of one another. An example of independent component placement systems and methods is described in U.S. patent application Ser. No. 11/684,514, filed Mar. 9, 2007, published as Pub. No. 2008/0058945, and hereby incorporated by reference herein in its entirety. One disadvantage of such systems is the determination of the placement of each implant component is not constrained based on the other implant components. Multiple component implant systems, however, often require that a number of relative constraints between the components be satisfied so that the implant system functions properly. If all implants are planned independently, it is nearly impossible to satisfy all the necessary constraints. For example, in order to have a smooth transition between the femoral condyle implant and the patella implant, the relative position of the two implants to each other is critical.
Further, proper placement of the implant components on the femur and tibia require knowledge of the articular cartilage surfaces of each bone. Articular cartilage is an avascular soft tissue that covers the articulating bony ends of joints. During joint motion, cartilage acts as a lubricating mechanism in the articulating joints and protects the underlying bony structure by minimizing peak contact force at the joint. A model of each bone can be generated from a CT scan of the bone to allow models of the implant components to be positioned relative to the bone models to plan for the surgery. However, CT scans may not accurately determine the articular cartilage surface of the bone. As a result, the planned placement of the implant components match only the surface of the bone and not the cartilage, while the surface of the cartilage frequently determines the optimal placement of the implant. Cartilage surfaces can be determined by capturing the tip positions of a tracked probe while the probe is dragged over the cartilage surface. However, this requires that each point is captured to draw the cartilage surface, which is a timely and computationally involved procedure.
In view of the foregoing, a need exists for surgical methods and devices which can overcome the aforementioned problems so as to enable intraoperative implant planning for accurate placement and implantation of multiple joint implant components providing improved joint performance; consistent, predictable operative results regardless of surgical skill level; sparing healthy bone in minimally invasive surgery; achieving a fit of the implant components that address each patient's unique anatomy, ligament stability, and kinematics; and reducing the need for replacement and revision surgery.